If you want to package up Haskell code to be called from other languages,
such as Visual Basic or C++, there are some extra things it is useful to
know. The dirty details are in the Foreign Function
Interface definition, but it can be tricky to work out how to
combine this with DLL building, so here's an example:

Use foreign export declarations to export the Haskell
functions you want to call from the outside. For example,